There is a floppy disc device as an external memory device used in an information processing apparatus such as a computer or the like. This floppy disc device uses a magnetic sheet as the recording medium. The magnetic sheet is called a disc, which is formed by a polyester substrate coated with a magnetic material and abounds in flexibility. Usually, the disc is contained in a jacket and this is called a floppy disc or a disket. An example of the prior art for mounting the disc on the floppy disc device is shown in FIGS. 1 and 2 (cross-sectional views) of the accompanying drawings. In FIG. 1, the disc 1 is positioned as shown relative to a rotary shaft 2 by inserting the disket (not shown) leftwardly (or rightwardly), but in this state the center 1a of the aperture portion of the disc and the center of rotation 2a of the rotary shaft are only roughly positioned and usually are not coincident with each other. Next, when a flange 3 is urged in the direction of arrow 4, a keep member 8 is lowered through a spring 5a, a bearing 6, a tapered piece 7 and a spring 5b. At this time, the keep member 8 depresses a pin 9a, so that a guide member 9 is also lowered along a guide bar 10. Therefore, the keep member 8 fits in the aperture portion of the disc 1. The disc 1 is held between the rotary shaft 2 and the flange portion 8a of the keep member 8. Next, when the flange 8a is further urged in the direction of arrow 4 as shown in FIG. 2, the spring 5b flexes to lower the tapered piece 7 and the tapered portions 6a and 7a of the tapered piece 7 are brought into contact with the inner surface of the keep member 8 to laterally widen the outer peripheral portion of the keep member 8 (the outer peripheral portion of the keep member 8 including the flange portion 8a is provided with a cut-away so that the outer peripheral portion of the keep member is laterally widened). At this time, the center 1a of the aperture portion of the disc 1 is corrected so as to be substantially coincident with the center 2a of the rotary shaft 2. However, in such a device of the prior art, the disc 1 in its state of being held between the rotary shaft 2 and the flange portion 8a of the keep member as mentioned previously is forcibly moved and therefore, wear tends to occur because of the disc 1 slipping relative to the rotary shaft 2. Also, when the slip can hardly take place (namely, when the frictional resistance is great), the aperture portion of the disc 1 may be damaged by the keep member 8. Accordingly, the aperture side of the disc 1 and the peripheral portion thereof are remarkably injured in proportion to the frequency of the above-described operation (mounting of the disket). The disc has an area in which recording and reproduction of information is effected (hereinafter referred to as the tracks), and the position of these tracks is displaced by the damage of the aperture portion of the disc, thus hampering the recording and reproduction of the information. When the aperture portion of the disc is so damaged, the disc becomes actually unusable due to the unsatisfactory positional accuracy of the tracks even if the magnetic surface of the disc is sufficiently usable.
It is therefore a first object of the present invention to accurately fix a leaf member at a predetermined position.
It is a second object of the present invention to prevent the leaf member from being damaged and to increase the life of the leaf member.
It is a third object to achieve the first and second objects by a simple construction and to suppress the rise of the manufacturing cost.